Fiber-reinforced plastics (FRP) have been attracting interest in recent years as lightweight, high-strength materials for various industrial fields. Fiber-reinforced composite materials comprising reinforcing fibers such as glass fibers, carbon fibers and aramid fibers in a matrix resin have lighter weights than rival metals, while also exhibiting excellent dynamic properties such as strength and elastic modulus, and they are therefore being employed in numerous fields such as aircraft members, spacecraft members, automobile members, ship members, civil engineering construction materials, and sports goods. In particular, carbon fibers, which have excellent specific strength and specific elastic modulus, are commonly used as reinforcing fibers for purposes in which high performance is required. Thermosetting resins such as unsaturated polyester resins, vinyl ester resins, epoxy resins, phenol resins, cyanate ester resins and bismaleimide resins are widely used as matrix resins, among them epoxy resins are commonly used because of their excellent adhesion with carbon fibers. Recently, a vacuum impregnation molding method (Vacuum assist Resin Transfer Molding: VaRTM) in which fiber-reinforced plastics are molded under reduced pressure conditions with vacuum suction, is being employed for low-cost production of relatively large fiber-reinforced plastic molded articles (see PTL 1 listed below, for example).
Such techniques are suitable for increasing the heat resistance and strength of resins, but the application of such techniques has been difficult because, for instance, it has not been possible to reduce the fiber diameters of the fibers themselves in order to achieve the size and thickness reduction of electronic materials needed to conform to recent trends toward increased functionality in the field of electronic devices. Moreover, electronic components must exhibit properties such as excellent low thermal expansion and low warping properties, in order to adapt to the reduced rigidity of substrates that is a consequence of their smaller thicknesses, and low dimensional deformation or warping when parts are connected to metal-clad laminates or printed circuit boards by solder reflow.
In addition, the mounting of such electronic components in vehicles is accelerating, and there is a demand for circuit boards with superior properties that can withstand use in extreme weather and high-humidity environments. PTL 2 describes an effect allowing provision of a circuit board that is lightweight and resistant to cracking, with minimal generation of CAF (Conductive Anodic Filaments) and smearing during the via hole-forming step, as well as a low filler filling factor and low linear expansion. It is a goal to ensure an excellent embedding property with greater moisture proofness, and to maintain embedded flatness and increase thermal shock resistance, when electrodes are embedded in resin composite films, to a level exceeding that of conventional electronic components as described in PTL 2, in particular with suitability for on-vehicle purposes.